This invention relates to a magnetic disc cartridge comprising a casing and a magnetic disc with a center core which is contained in the casing, and more particularly to a dust-proof structure for a lower side of the casing where an opening for giving access to the center core is formed.
There has been known a magnetic disc cartridge comprising a casing formed of upper and lower casing halves and a magnetic disc supported for rotation in the casing. High reliability is required when information is recorded on the magnetic disc and reproduced from the magnetic disc by use of a disc drive system.
For example, it is important that the magnetic disc and/or the magnetic head are kept free from dust which causes so-called drop-out. Dusts include those generated inside the casing and those entering the casing from the exterior through openings in the casing.
A center core opening for giving access to the center core to a spindle of the disc drive system is formed on the lower side of the casing and is normally kept opened. Dusts which enter the casing through the gap between the center core opening and the center core are more apt to give rise to a problem.
Further, as the packing density of the magnetic disc is increased, the line recording density and the track density are increased. Accordingly just a small of amount of dusts adhering to the surface of the magnetic disc can cause drop-out, and there has been a demand for higher dust-proof performance.
In conventional magnetic disc cartridges containing therein a magnetic disc whose recording capacity is relatively small, a liner such as of unwoven fabric is provided on the inner surface of the casing and the liner is brought into contact with the surface of the magnetic disc by a lifter to wipe off dusts on the magnetic disc.
However in the case of a larger capacity magnetic disc cartridge, the magnetic disc is rotated at a higher speed in order to increase the data transfer speed. In order to stably rotate the magnetic disc at a high speed, it is preferred that the torque be reduced. For this purpose, there is a trend to reduce the contact pressure between the liner and the magnetic disc. Further there is a trend to omit the liner in order to suppress generation of dusts inside the casing. Thus entry of dust into the casing must be prevented more strictly.
As the rotating speed of the magnetic disc is increased, an air flow from the central portion of the magnetic disc toward the outer edge of the magnetic disc is generated by centrifugal force in response to rotation of the magnetic disc and the pressure inside the casing becomes low at the central portion thereof, which introduces air into the casing through the center core opening. Since the air introduced into the casing through the center core opening carries dusts, measures for preventing entry of dusts through the center core opening are effective.
Though entry of dusts through the center core opening can be prevented by providing a shutter member for opening and closing the center core opening, this approach will give rise to a problem in ensuring so-called xe2x80x9cdownward compatibilityxe2x80x9d.
That is, a disc drive system for a larger capacity magnetic disc cartridge is generally arranged to be capable of driving a conventional magnetic disc cartridge as well as the larger capacity magnetic disc cartridge. This is generally referred to as xe2x80x9cdownward compatibilityxe2x80x9d. When the disc drive system for a larger capacity magnetic disc cartridge is provided with such xe2x80x9cdownward compatibilityxe2x80x9d, it is preferred that the disc drive system can drive either of the magnetic disc cartridges by a single mechanism. Form this view point, it is disadvantageous that the larger capacity magnetic disc cartridge is provided with a shutter member for opening and closing the center core opening.
In view of the foregoing observations and description, the primary object of the present invention is to provide a magnetic disc cartridge in which the dust-proof performance is increased without interfering with downward compatibility.
The magnetic disc cartridge of the present invention comprises a magnetic disc with a center core and a casing which contains therein the magnetic disc for rotation and is provided in its lower side with a center core opening for giving access to the center core to a disc drive member of a disc drive system, and is characterized in that a cover member which covers the space between the center core opening and the center core is provided on the lower side of the casing.
Typically, the cover member is a ring-like member of a resilient material such as a plastic sheet. When the cover member is a ring-like member, the outer diameter of the cover member should be larger than the inner diameter of the center core opening, and the inner diameter of the cover member should be smaller than the outer diameter of the portion of the center core exposed through the center core opening so that the cover member covers at least the space between the center core opening and the center core. It is preferred that the inner diameter of the cover member be selected so that a drive hole which is formed in the center core to be brought into engagement with a drive pin of a disc drive system is not closed by the cover member even if the center core is positioned off-centered with respect to the center core opening.
It is preferred that the cover member be received in a recess formed in the lower side of the lower casing half so that the lower surface of the cover member is positioned flush with the lower side of the lower casing half.
In the magnetic disc cartridge of this embodiment, the cover member prevents entry of dusts through the space between the inner peripheral edge of the center core opening and the center core, whereby adhesion of dusts to the surface of the magnetic disc is suppressed and generation of drop-out is suppressed, which increases the reliability of the magnetic disc cartridge. Further, since the structure of the center core and the center core opening is the same as that in the smaller capacity magnetic disc cartridge, the disc drive system for the magnetic disc cartridge of this embodiment can also drive the conventional magnetic disc cartridge without additional drive mechanism, that is, downward compatibility can be easily ensured.